This invention relates to an apparatus and method that forms a flexible bag, fills it with a slurry composition, and seals the bag for shipping. More specifically, it relates to a form-fill-seal apparatus that quickly and accurately fills the bag to an appropriate weight.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are conventionally constructed by affixing the panels to studs or joists, and then filling and coating the joints between panels with a specially prepared composition called a joint compound. This process generally proceeds by placing a taping grade joint compound within the joint formed by the abutted edges of the wallboards and embedding a liquid-permeable tape within the taping compound. When dry (or set), a second coating comprising a topping grade joint compound is applied over the joint. This is sanded lightly, then a third coat applied and conventionally finished. Another grade of joint compound is an all-purpose grade that is used both for embedding the tape and for applying the finish coats. A patterned effect may be given to the finished wall and joint with the all-purpose joint compound to provide a textured finish.
There are two general types of joint compound, setting type and drying type. Joint compound of the setting type sets up and becomes firm when hydration reactions convert calcium sulfate hemihydrate and water into an interlocking matrix of calcium sulfate dihydrate crystals. Excess water evaporates. Drying type compound becomes firm upon the loss of water by evaporation.
Each form of joint compound is sold either as a dry powder mix or in the form of an aqueous slurry. The dry powder includes either calcium carbonate or calcined gypsum and dry forms of appropriate additives. Each form has its advantages depending on what is available at the job site. The dry mix requires the transportation of less material. However, it requires the availability of both water and mixing equipment. Where these materials are not readily available, or where the job is so small that it is inconvenient to obtain them, a ready-mix joint compound may be the most suitable form of joint compound to use.
Preparation of a ready-mix, setting type joint compound requires additional chemical components compared to a drying type joint compound or a dry mix. However, once water is added to the calcined gypsum, the setting process begins unless it is prevented chemically. Set retarders are added in sufficient quantities to prevent hardening. Prior to use, a set accelerator is added to the ready-mix joint compound to overcome the effects of the set retarder. If a drying-type joint compound has water added, hardening of the slurry can be delayed if the water is not permitted to evaporate. Keeping a drying-type joint compound tightly sealed is sufficient to keep it in a slurry form.
Slurry products have been a challenge for packaging specialists. The product is very heavy due to the weight of the water. It is fluid within the packaging, allowing the weight distribution to shift. If the packaging is ruptured or punctured, slurries tend to leak out, making a mess of other product in the vicinity. Conventionally, ready-mix joint compounds have been packaged in either a plastic pail or a plastic-lined carton. The hard exterior of these packages provides rupture and puncture protection to the product, it gives support to the heavy slurry and it provides a package that is easier to stack on a palette without shifting.
However, these forms of packaging are very expensive compared to a plastic bag. In addition to the cost of the packaging materials, additional equipment, including carton formers, bag inserters, carton sealers, lid placers, doily placers and lid sealers are needed to complete the packaging. Additional labor is needed to operate and maintain these extra machines. The collective footprint of the packaging equipment is large, requiring a large facility and the accompanying capital investment.
Some prior art filling machines form the bag and transfer most of the product to the bag at one station, then move the bag to a second station to be topped-off accurately. Time and additional equipment are needed to move a partially filled bag of slurry to the second filling station. Movement of the bag provides opportunities for spillage or damage of the bag as well. While topping and sealing the bag at a second fill station may save a bit more time at that the first station, the total time needed to fill the bag including transfer time is not necessarily reduced, and it introduces opportunities for product damage. There will also be a cost associated with additional personnel to operate and maintain the extra equipment.
The prior art reveals little about packaging of slurry compositions. Plastic bags are frequently used for packaging of powdered or granular materials greater than 100 microns in particle size. Joint compound slurry has been packaged in a tube as in U.S. Pat. No. 4,436,204. The joint compound is pumped into the tube. Air is removed from the tube and it is tied or crimped shut. A humectant is sprayed in the inside of the package of ready-mix joint compound to maintain uniform moisture content in U.S. Pat. No. 5,323,588. In U.S. Pat. No. 5,413,154, granular materials are fed by an auger into a gravity fed delivery conduit. A custom product mix is obtainable by programming selected quantities of materials, selected proportions or selected rates. The materials are fed to a transfer line which then moves to a delivery location where the blend is placed in containers. Slurries, such as drilling muds, are optionally made by the addition of a liquid to the granular product.
There is a need in the art for a low-cost packaging alternative to plastic pails and lined cartons for ready-mix gypsum products. There is also a need for a packaging line that accurately measures the product sold by weight. There is yet another need for a packaging system and method that takes up little space and can be operated by a minimum of personnel.